Disruption blamed on attacks on power pylons means large parts of region annexed by Russia are without electricity.
People living in the annexed Russian region of Crimea have been without a reliable source of electricity for three days now.
Power lines supplying the breakaway Ukraine region were blown up over the weekend and people are having to rely on handouts.
Alexander Novak, Russia’s energy minister, has accused the Ukrainian authorities of deliberately refusing to help rebuild the power lines, which were blown up by unknown saboteurs.
Reports said the peninsula of two million people is relying on emergency generators to meet its basic power needs, with pro-Ukrainian activists, including nationalist battalions and ethnic Tatars, preventing repairs.
The Ukrainian government dismissed as “absolutely groundless” suggestions, made by two Ukrainian lawmakers to Reuters, that Ukraine might be tacitly backing the activists.
The row could inflame tensions between Ukraine and pro-Russian fighters in the east, where a recent surge in ceasefire violations is threatening to shatter a truce after two months of relative calm.
The incident has also prompted Russia to issue a threat to Ukraine, that it would cut off gas supplies and halt coal deliveries to Ukraine.